1. Field of the Invention
The present invention relates to a fiber article having excellent hydrolysis resistance and containing a biodegradable plastic, and more specifically relates to a fiber article having excellent hydrolysis resistance, alkali resistance, and dyeing resistance, by formulating a stabilizer against hydrolysis comprising a carbodiimide compound to a fiber using a biodegradable plastic.
2. Description of the Prior Art
As a biodegradable plastic degradable by an enzyme or a microbe, an aliphatic polyester is noted, and as the biodegradable aliphatic polyester, polylactic acid, polyglycolic acid, poly(3-hydroxybutylate), poly(3-hydroxybutylate-3-hydroxyvalerate), polycaprolactone, and a polyester comprising a glycol such as ethylene glycol, 1,4-butanediol, and the like and a carboxylic acid such as succinic acid, adipic acid, and the like are known.
However, these aliphatic polyesters have very high hydrolytic property in water at room temperature or high temperature, and further have tendency to be degradable even by moisture in atmosphere. Due to the above nature to be easily degradable, there were various problems as follows. For instance, when they are used as fibers, dyeing at high temperature in an aqueous solution dispersed with dye abruptly decreases tear strength of a cloth, and thus only dyeing under comparatively low temperature condition is allowed, which in turn makes deep color dyeing impossible. Furthermore, when they are used in water for marine materials such as a fishermen's net, service life thereof is limited to extremely short period. Furthermore, since they have poor stability with elapse of time, they cannot exhibit initial performance owing to deterioration after elapse of long period after production.
To solve such problems as above, technique to cap terminal carboxylic groups of polylactic acid, which is a sort of an aliphatic polyester, by a condensation reaction with an aliphatic alcohol, is disclosed (for example, see JP-A-7-316273 (Claims and the like)).
However, the technique of capping terminal ends is a condensation reaction, and to remove reaction byproducts, it is necessary to the presence of an aliphatic alcohol together in polymerization of the polylactic acid, and there have been such problems as follows. Polymerization rate thereof is low, and accordingly industrial production is impossible, or many unreacted materials having low molecular weight reside, and since they vaporize in molding, appearance of a molded article is inferior, or thermal resistance of the article is poor. Further, there has been such a problem as, during re-melting and molding a polymer (a chip) having capped terminals, which polymer has been obtained by a condensation reaction, terminal carboxylic groups are regenerated, and uncapped terminal ends occur, which makes hydrolysis resistance of molded articles insufficient.
Moreover, technique is disclosed to decrease concentration of terminal carboxylic groups of polylactic acid fiber, by lowering spinning temperature, in addition to capping of terminal carboxylic groups with an aliphatic alcohol (for example, see JP-A-9-21017 (Claims and the like)).
However, because melt viscosity of an aliphatic polyester represented by polylactic acid has relatively high dependency on temperature, there has been a problem that it is necessary to decrease molecular weight of a polymer sufficiently in response to spinning at low temperature, and thus polylactic acid fiber having sufficiently high strength as a commonly used fiber, and the like cannot be available.
On the other hand, to improve hydrolysis resistance, technique to formulate a carbodiimide compound with a biodegradable plastic, is disclosed (for example, see JP-A-11-80522 (Claims and the like)).
However, with a mono-carbodiimide compound disclosed in Patent Reference 3, there has been such a problem as insufficient thermal resistance, that means, thermal degradation is apt to occur during processing, which causes environmental pollution owing to occurrence of stimulative smell components and decrease in the addition effect owing to vaporization.
To improve this, a polycarbodiimide compound is used, but there was a problem of coloring (yellowing) in processing, and therefore it has been difficult to use in applications where hue is made much of (for example, use of a fiber for clothing).
Further, when a fiber comprising a biodegradable plastic is processed for dyeing, there has been such a problem as remarkable decrease in strength of the fiber comprising a biodegradable plastic.
From such situations, some proposals have been made to improve hydrolysis resistance of a biodegradable plastic or a fiber comprising the same. For instance, an aliphatic polyester resin such as polylactic acid and a molded article such as a fiber or a film comprising the same, characterized in that a part of or substantially whole of terminal carboxyl groups in an aliphatic polyester is capped with a mono-carbodiimide compound having temperature of 5 wt % decrease of not lower than 170° C. as measured by TG-DTA (for instance, concentration of terminal carboxyl groups is not higher than 10 equivalents/103 kg of an aliphatic polyester) (see JP-A-2001-261797 (Claims and the like)); and a fiber of polylactic acid having excellent hydrolysis resistance, wherein terminal carboxyl groups thereof are capped with a poly-carbodiimide compound, characterized in that b* value, which is an index of color tone, is not higher than 7 (see JP-A-2003-301327 (Claims and the like)), are disclosed.
However, with an aromatic mono-carbodiimide compound as disclosed in JP-A-2001-261797 (Claims and the like), weatherability to sunshine, and the like is poor, which means unpractical. And in a fiber of polylactic acid wherein terminal carboxyl groups thereof are capped with a poly-carbodiimide compound as disclosed in JP-A-2003-301327 (Claims and the like), a problem of poor thermal stability (or thermal resistance) in fiber production is adjusted by spinning condition and by the addition amount of a poly-carbodiimide compound, however, this method had still a problem that appropriate condition range was narrow, resulting in not stable quality, and additionally insufficient levels of color hue stability (for example, yellowing) and hydrolysis resistance, which brought about no durability in dyeing processing of a fiber article conducted under the above-described acid and alkali conditions. There was also a problem of insufficient durability after producing an article.
Moreover, in the case of a fiber article by combination of a biodegradable plastic and a cellulose fiber, and the like, applying chances of liquid ammonium processing, silket processing (mercerization processing), dyeing processing, or bleaching processing seem to increase. However, with these processings, treatment with an alkali, an acid, chlorine, heat, and the like increases and especially by passing an alkali processing step, such a problem may happen as significant decrease in strength of a fiber article comprising a biodegradable plastic.
As above, conventionally, attempts to improve hydrolysis resistance have been challenged by decreasing concentration of terminal carboxyl groups in an aliphatic polyester, such as polylactic acid, but a fiber or a fiber article comprising an aliphatic polyester having both sufficient thermal resistance and hydrolysis resistance has not yet been attained.